Photographic sound recording system and aperture plate therefor



April 26, 1949. G. L. DIMMICK PHOTOGRAPHIC SOUND RECORDING SYSTEM AND APERIURE PLATE TH FOR Filed April l9, 19

- L INVENTOR.

620W 1, fl/mwcw Patented Apr. 26, 1949 PHU'IOGRAPHIC SUUND RECORDING SYS- ITEM AND APERTURE PLATE THEREFOR Glenn L. Dimmick, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 19, 1947, Serial No. 742,545

3 Claims.

1 This invention relates to sound recording equip- -ment,'and particularly to a method of and means for recording either a negative or direct positive sound record with the same recorder.

In-my U. S. Patent No. 2,311,159 of February 16, 1943, a method of and means for recording a direct positive type of sound record is disclosed and claimed. This patent describes a system "wherein the light is so impressed on the film that after the normal development thereof, the track =r record is in the form produced by printing from the-usual negative.

There are many advantages inthe direct recording of such a record without going through the printing operation step. There are also advantages in the recording of a negative, and the present invention discloses a system whereby the recorder can be very rapidly ad justed so that it will record either a negative or a direct positive record according to the adjustment of the modulating element.

In my copending application Serial No. 629,294, filed November 17, 1945 a system of the general type of this invention has been disclosed and claimed. However, with the advent of double bilateral and push-pull recording and reproduction wherein the record consists of two separated 1on- "gitudinal portions, the reproducing optical system utilizes beam splitting lenses which project =thelight from each longitudinal section of the record to each of two portions of a photoelectric cell or one of two separate cells. In such a beam splitting optical system there is a small narrow longitudinal portion of the track which cannot -be utilized because of the physical division or septum between the splitting optical cylinders. Thus, -ifa single section sound record is reproduced in a push-pull optical system, and parphotocell or a push-pull photocell reproducing system. That is, the two sections of the push-pull photoelectric cell are connected in parallel for the double bilateral type of record suchas made with the present invention, and then switched to a push-pull connection for regular push-pul1 tracks.

The principal object of the present invention,

therefore, is to facilitate the recording of film sound records.

Another object-of the invention is toprovidean improved recording method of and system .for producing either a direct positive or negative sound record with the same apparatus.

A further object of the invention is tQp ovide an improved sound recording aperture for recording either a negative or positive sound record which isreproducable in any type of reproducing sound system.

A still further object of the invention is .to provide a sound recording system which maybe rapidly changed from a negative to a directpositive system, or vice versa, the recordof whichls reproducable in either a single photocell or pushpull reproducer.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description readin conjunction with the accompanying drawing, forming a part hereof, in which:

Fig. 1 is a diagrammatic view of a recording system embodying the invention;

Fig. 2 is a plan view of the slit mask showing .a light beam superimposed thereon;

Fig. 3 is a section of the negative soundtrack made in accordance with the inventiomand Fig. 4 is .a section of a direct positive sound track made .in accordance with the invention.

Referring now to the drawings in which the same numerals refer to like elements, the output ofa microphone 5 is fed into an amplifier 5, and then directly over conductors l to a galvanometer .8. .The output of amplifier 6 is also fed to. av noise reduction amplifier Ill, and then overv conductors I I to the galvanometer 8, it being well understood that the galvanometer mirror [2 is vibrated both in accordance with the instantaneous values-of the sound waves and the envelope of the sound waves. Theremaining portion. of the recording systemincludes a light source [4, a collectinglens .l5,.a mask plate It, and a lens .l8, together with ,a.1ens,20,.-a slit mask plate 21, a lens Rania film'22. In such a system, light from the lamp M is formed into a W shaped lightbeam by the aperturelzdin themask. l6, thenprojected on the ,mirror l2,ofthe galvanometerfi from which itjs reflected to the slit mask 2|, the light emerging through a slit 26 and slits 21 and 28 being impressed on the film 22, as will now be described.

Referring now to Fig. 2, the slits 26, 21 and 29 are shown in the mask 2| together with the superimposed W shaped light beam shown by the lined portion 30. The aperture has irregular side edges and parallel end edges. In the position of the light beam in this figure, fifty percent of the slit 26 is illuminated. However, because of the noise reduction bias, the no signal or zero position of the light beam is such that only the tip portions 0. and b of the beam pass the slit 23 to produce the so called bias lines. As the amplitude of the signal increases, the output of the noise reduction amplifier I moves the average position of the beam downwardly in accordance with the envelope of the signal as the beam vibrates in accordance with the instantaneous values of the signal. The result of this type of recording produces a double bilateral record such as shown in Fig. 3, wherein the light impressed on parallel portions 40 and 4| of the sound record are opaque when developed and the remaining portion of the sound track area of the film is transparent. When this film is printed, however, the reverse densities occur on the print as is well known in the art. To illustrate the length of the slit 2%? as projected on the film, a section 42 of the modulations are shown overshot, the slit length being represented by the distance between the flat ends.

Referring again to Fig. 1, the position of the galvanometer 8 is controlled by a manual screw 32, the galvanometer being adapted to pivot in any suitable manner, such as on or about point 33. With the galvanometer adjusted by the screw 32 so that the light beam 3!] is impressed on the slit plate 2! with respect to the slit 26, as shown by the lined portion in Fig. 2, a negative type of record, as shown in Fig. 3, will be produced. It will be noted that the perpendicular distance between the ends of slit 26 and the lower points of the light beam 38 is the same as the distance between the slit 26 and the slits 21 and 28. Thus, no light will pass through the slits 21 and 28, even during overloads up to one hundred percent, such overloads usually being prevented by the limitations of the galvanometer and the ampli- Now, if it is desired to record a direct positive type of record, such as shown in Fig. 4, and which will be the same as the print made from the negative shown in Fig. 3, it is only necessary to tilt the galvanometer 8 slightly by the screw 32, so that the light beam 30 assumes the position shown by the dotted lines 35 in Fig. 2. It will be observed that when the beam is in position 35, the slit 26 again passes light along fifty percent of its length, but the light now passes the slit at its ends and central portion rather than in its former portions. It will also be noted that light is now projected through slits 21 and 28. However, because of noise reduction bias, at times of no signal, or zero position of the light beam, light is passed by the entire slit, except for two short, narrow portions corresponding to the points shown by the bias lines a and 17, light being passed by slits 21 and 28 at all times. This adjustment of the galvanometer can be made very rapidly, while the noise reduction adjustment, or bias, is always for the same amount and in the same direction, regardless of the type of record to be recorded.

The result of the shifting of the galvanometer so that the light beam 30 takes the position ill shown by the dotted lines is a record such as shown in Fig. 4, wherein the two modulated portions 43 and 44 will be transparent and the remaining portion, up to the outer ends of slits 2'! and 28, will be opaque upon the development thereof. To again illustrate the length of slit 26, overshooting of the section 45 is shown similar to section 42 in Fig. 3.

In Fig. 1, two vertically elongated apertures 38 and 39 are shown through which light from the source I4 is projected and after modulation by the mirror I2 is projected on a mirror 31 posi tioned near the end of the slit plate 2|. This light may be used for monitoring in the manner disclosed in my copending application Serial No. 629,295, filed November 17, 1945, or the slit mask 2| may have a window therein through which the monitoring beam is projected and reflected to an observation medium in accordance with a system shown in L. T. Sachtleben copending application Serial No. 742,360, filed April 18, 1947. The upper monitoring aperture 38 is used when monitoring the recording of a negative record, and the lower aperture 39 is used when monitoring the recording of a positive record, as disclosed in my above mentioned copending application.

I claim:

1. A sound recording system adapted to record different types of sound tracks comprising a source of light, means for forming light from said source into a beam, a vibrator for said light beam, a film on which portions of said light beam are impressed, and a mask having a light slit therein for determining the portions of said beam impressed on said film, said first mentioned means including a mask having a W-shaped aperture therein, light passing one irregular edge of said W-shaped aperture recording a negative type of record and light passing the other irregular edge of said W-shaped aperture recording a direct positive type of record, the spacing of said edges of said beam being greater than the movement of said beam at said slit mask during the recording of one of said records.

2. A sound recording system in accordance with claim 1 in which double bilateral sound records are produced by said recordings.

3. A sound recording light-shaping aperture plate for recording either a double bilateral negative record or a double bilateral positive record comprising an opaque plate having an opening therein in the shape of the letter W, the ends of the aperture having edges parallel to one another and perpendicular to the, longitudinal axis of the aperture, the Width of the aperture between the irregular edges of the W being substantially one-half of the length of the aperture along the longitudinal axis thereof.

GLENN L. DIMMICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,653,836 Berglund Dec. 2'7, 1927 1,999,721 Dimmick Apr. 30, 1935 2,044,188 Soto June 16, 1936 2,268,438 Batsel Dec. 30, 1941 

